Oscillation system



pxrl 7 R36., N, P. CASE OSCILLATION SYSTEM Filed sept. 28, 1955 ma /U HM n FU. Z f W 0 0 D "7l INVENTOR.

ATTORNEY.

Patented Apr. 7, 1936 PATENT OFFICE OSCILLATIGN' SYSTEM Nelson P. Case, Great Neck, N. Y., assigner to Hazeltine Corporation, a corporation of Dela- Application September 28, 1935, Serial No. 42,602

18 Claims. (0l. Z50-36) This invention relates to tuned systems and particularly to composite tuned systems or oscillation circuits for oscillators arranged to operate in either of two or more bands of frequencies, such as the local oscillators of multi-band superhetercdyne receivers.

. A composite tuned system, made up of two or more closed circuits which have one or more common reactance elements, generally has a principal resonant frequency determined by all of the reactance elements of such system and one or more other or spurious resonant frequencies determined by groups of less than all of said reactance elements, such as by the reactance elel5 ments in either closed circuit alone. It has been found that under certain circumstances a tuned system of such a character tends to oscillate, and in many cases actually does oscillate, at one oi such spurious frequencies when it is desired to have the system osoillate only at its principal resonant frequency. More particularly, it has been found that, when a tunable multi-band superheterodyne receiver is adjusted to receive signals in certain portions of one or more of their signal frequency bands, the local oscillator thereof tends to jump from the frequency at which it is intended to operate to a spurious frequency, thereby eiectively preventing reception.

It is an object of this invention to provide a method of, and a means for, preventing spurious oscillations in a composite tuned system of the type described.

It is another object of the invention to provide a tunable multi-band oscillator in which any tendency of the oscillations thereof to jump to a spurious frequency is eiectively prevented.

Other objects of the invention will become apparent from a consideration of the following specification, taken in conjunction with the accompanying drawing and the appended claims.

The invention contemplates a composite tuned system made up of two or more component resonant circuits having one or more common reactance elements, the principal resonant frequency being that for the composite tuned system. In order to insure that the composite systern oscillates only at such principal frequency,`

and not at the resonant frequency of one or more or" the component circuits,`the power factors of 5o such one or more component circuits are modified so that the power factor of each of such component circuits is greater than the power factor of the composite system.

In the drawing, Fig. l is a circuit diagram of 55 -a tunable multi-band oscillator illustrating the invention as applied thereto; and Fig. 2 is a circuit diagram, partly schematic, illustrating the f invention as embodied in a multi-band superheterodyne receiver.

Referring to Fig. 1, the oscillator there shown 5 comprises a vacuum tube Il, an oscillation system I 2 and a feed-back coil i3. The oscillation system I2 comprises two serially-connected inductance elements i4 and l5 across the exterior terminals of which is connected a variable tun- 10 ing condenser I6. Inductance elements M and it are individually shunted by two relatively small trimmer condensers il and it, respectively. Inductance element it may be effectively shortcircuited bya switch 2. Series-connected align- 15 ing condensers 22 and 23 are also included in the oscillation system, between a low potential end of inductance element it and the grounded terminal of the tuning condenser it.

Oscillation system it is effectively connected 20 across the grid-cathode circuit of tube li, condenser 215 and resistor 25 being the customary grid condenser and grid leak, respectively. The feed-back coil it, coupled to the anode of tube lll by a coupling condenser 2li, is inductively re- 25 lated to both inductance elements itl and it.

The oscillator with the oscillation system described is tunable over two different frequency bands, operation in the higher frequency band occurring when switch it is closed, at which time 30 the oscillator frequency is determined by the resonant frequency of the tuned circuit composed of inductance element l5 and condensers it, it and 23. When switch 2li is opened, as illustrated, the oscillator operates in the lower frequency 35 band, with the oscillation frequency determined by the entire oscillation system comprising inductance elements it and i5 and condensers "l, it, it, i2 and 2t.

In the higher frequency band condensers it 4,0 and 23 serve, respectively, as paralleland seriesaligning condensers, and in the lower frequency band condensers 'l and 22 serve, respectively, as the principal paralleland series-aligning condensers, in each case in a manner well known 45 in the art. 'Ihe condenser 23 serves also as an additional coupling or feed-back element between the anode circuit and the oscillation system, as disclosed and broadly claimed in United States Letters Patent No. 2,007,253, granted July 9, 1935, upon the application of William A. Mao- Donald, and is' effective to maintain the amplitude of the oscillations within desired limits over the tuning range of the system. Inductance elements i4 and l5 may be of any suitable value. 55

Since, however, variable condenser I6 customarily has a fairly wide range of capacity variation, inductance element I4 generally has a substantially greater inductance than inductance element I5 in order that the overlap; if any, of the two bands over which the oscillator is tunable may be small.

It has been found that, when the oscillator is arranged for operation in the lower frequency band (with switch 20 open) and variable condenser I6 is set to a low capacitance so as to tune the oscillator to a frequency in the upper portion of such lower frequency band, the oscillator has a tendency to operate at a frequency determined, not by all the reactance elements then effectively included in the oscillation system I2, but at a frequency determined by only a portion of such elements and in particular at the resonant frequency of the closed circuit including inductance element I4 and condenser I1. This tendency becomes more pronounced as the capacitance of tuning condenser I6 is decreased. When the oscillator changes its frequency of operation from the desired frequency determined by all the inductance elements effectively included in oscillation circuit I2 to the spurious frequency determined by inductance element I4 and condenser I1, this change is effected very suddenly and is commonly known as jumping".

To overcome this tendency of the oscillator to jump to a spurious frequency, in accordance with this invention, there is provided a resistor 21 in the closed circuit including inductance element I4 and condenser I1, the resistor 21 being so proportioned that the power factor of such closed circuit is greater than that of the complete oscillation system I2, even when the latter is tuned in the upper portion of the lower frequency band. This insures that any oscillation at the spurious frequency is attended with greater expenditure of energy than is oscillation at the desired frequency. As a consequence, the oscillator loses its tendency to oscillate at the spurious frequency.

Preferably resistor 21 is connected, as illustrated, in the capacitative leg of the closed circuit I4, I1. The resistor 21, while thus effectively in series in such closed circuit, is not substantially effective in the oscillation circuit as a whole, particularly in the other portions of the band, inasmuch as, at the frequencies to which the oscillation circuit is tunable, the impedance of the capacitive branch of such closed circuit is appreciably higher than the impedance of the inductive branch thereof. Resistor 21, therefore, serves substantially to increase the power factor of such closed circuit while not substantially increasing the power factor of the oscillation system as a whole.

Fig. 2 illustrates the invention as applied to the local oscillator of a multi-band superheterodyne receiver. In such receiver, an antenna circuit 30 is connected to a radio-frequency selector and amplifier 3l which may be of any suitable type, including a plurality of inductance coils (not shown), selectively connected by a switching mechanism 32, in circuit with a variable tuning device 33 to form a plurality of circuits severally tunable over different bands of signal frequencies. The output of the selector and amplifier 3| is connected through a multi-band coupling system 34 to the signal input circuit of an oscillator-modulator tube 35 provided with an oscillation svstem 31. In cascade with the oscillatormodulator 35 are an intermediate-frequency ampliiier 40, a detector and automatic amplification control source 4l, an audio-frequency amplifier 42, and av sound reproducer 43. The automatic amplification control bias potential may be applied to any one or more of the radio-frequency selector and amplifier 3|, the oscillator-modulator 35, and the intermediate-frequency amplifier 40, as desired.

The illustrated multi-band coupling system 34 comprises a primary inductance element 5D, three series-connected secondary inductance elements 5I, 52 and 53 inductively related to primary element 50, and a variable tuning condenser 54 connected across the exterior terminals of the seriesconnected inductances 5I, 52 and 53, the low potential side of condenser 54 being connected to the low potential terminal of inductance element 5I through coupling and series-aligning condenser 55. Three adjustably fixed trimmer condensers 56, 51 and 58 are connected in parallel with inductance elements 5I, 52 and 53, respectively. Inductance elements 5I and 52 may be effectively selectively short-circuited by a switch in a Well-known manner. An open-circuited winding 63, connected to the high potential end of primary inductance element 50 and related, principally capacitively, to secondary inductance element 53, is preferably provided to improve the transfer of the coupling system in the highest band of frequencies.

Oscillation system 31 comprises three serial-lyconnected inductance elements 66, 61 and 68 across the exterior terminals of which is effectively connected a variable tuning condenser 10, the low potential terminal of inductance element 66 being connected to the grounded side of tuning condenser 10 through three series-connected condensers 1I, 12 and 13. Effectively connected in shunt across the respective inductance elements 66, 61 and 68 are adjustably fixed trimmer condensers 16, 11 and 18, the circuit of condenser 16 being completed through a switch 80 and condensers 12 and 1I. Included in the capacitive shunt across inductance element 61 is a resistor 19, serving the same purpose as the resistor 21 of Fig. 1. Switch. 80 and a companion switch 8l are arranged to selectively effectively short-circuit inductance element 66 or both inductance elements 66 and 61. and 8I are preferably ganged for unicontrol, as indicated by the dotted lines 82. Likewise, variable condensers 33, 54 and 161 are preferably ganged for unicontrol, as indicated by the dotted lines 84.

Oscillation system 31 is effectively connected across the oscillator grid-cathode circuit of tube 35 through a grid condenser 85 and a grid leak 86, and a cathode biasing resistor 81 and by-pass condenser 88.

The oscillation-producing coupling, or feedback, for oscillation system 31 is provided by a winding connected in the oscillator anode circuit of tube 35 and inductively related to inductance elements 66, 61 and 68, and by the aligning and coupling condensers 12 and 13, the condenser 13 acting alone in the high-frequency range. To assist in maintaining high conversion gain at the high-frequency end of the high-frequency range, the oscillator-modulator is preferably .provided with a neutralizing capacitance, illustrated as a turn or two of insulated wire, 93, about the lead to signal input grid of tube 35 and connected to the high potential terminal of condenser 10.

Switches 32, 60,

In operation, the desired received signal is selected and amplified in radio-frequency selector and amplifier 3|, and further selected and transferred by the coupling system 34 to the oscillatormodulator tube 35, where the signal is converted into a modulated -intermediate frequency. The signal, as thus converted, is amplified in the intermediate-frequency amplifier 40, rectified by detector 4|, producing the audio frequencies of modulation, which are amplified in the audiofrequency amplifier 42 and reproduced by the sound reproducer 43.

The amplicationof the received signal is subject to automatic control by the AVC bias potentials, according to. the manner well understood in the art.

When the receiver is adjusted for reception in the middle-frequency range (at which time switches 32, 60, and 8l are in their middle positions) and particularly when the receiver is tuned to desired signals in the high-frequency portion of such range, the oscillation system 3l, in the absence of resistor 19, has a tendency to jump from the desired frequency determined leyl the composite circuit comprising inductance elements 61 and 68 and condcnsers ll, lil, lll, 1d and 'l2 to a spurious frequency determined by the component circuit comprising inductance element 6l and condensers ll, 13 and l2. This tendency is effectively minimized or eliminated by the action of resistor lil, which is so proportioned as to insure that the power factor of the component circuit is greater than that of the oscillation system as a whole. This tendency is further minimized over that which would be present if the low potential terminals of condensers lli and 'lil were connected directly to the low potential terminals of inductanceelements El and 68, respectively, (as illustrated for condensers il and l in Fig. 1), by connecting the low potential terminals of such condensers directly to ground, as illustrated in Fig. 2, so as to provide a greater effective impedance at the spurious frequency between the oscillator grid and the high potential terminal of the inductance eement (il.

When the receiver is adjusted for reception in the low-frequency range, the oscillation system has no tendency to jump from the desired frequency determined by the composite circuit cornprising inductance elements 66, tl and t8 and condensers lli, lll, lli, lil, i3, l2 and 'il to a spurious frequency determined by the component circuit comprising inductance element iid and condensers it, ll, 'l2 and lit. This is principally because inductance element t6 is of relatively large inductance, and thus in practice is a universal wound coil of relatively ne wire, with a resulting relatively high power factor. In contrast, inductance elements lil and 68 are generally single layer windings of larger wire, so that each has a relatively low power factor.

The methods and means for suppressing spurious oscillations disclosed and claimed herein are not limited to any particular frequency range, nor to oscillators used in superheterodyne receivers. In order to illustrate. however, the relative magnitudes of the various circuit elements of a typical circuit arrangement tending toward spurious oscillation and including means for preventing such oscillation, in accordance with this invention, the fol'owing approximate values for the oscillation circuit elements, and other pertinent information, are given for a receiver of the type shown in Fig. 2.

Received slzv- Oscillator irenal frequency quency Low-fre uency band. 13S-333 kc. 589-789 kc. Middlerequency band. 526-1532 kc. 982-1988 kc High-frequency band 5.5-l8.2 mc. 5 9048.66 mc Inductance element 68....- inductance element 67 inductance element 66..... 630 Do. Inductancc elements 67 and 68 126 Do. inductance elements 06,

an Condensers 77 and 78 25 micro-mlcrolsrads, maximum, generally adjusted between 3-10 mlcro-microlarads.

While I have described what I at present consider the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What is claimed is:

l. An electric circuitarrangement for preventing a composite tuned system, composed of a plurality of component tuned circuits having reactance elements individual thereto and a reactance element common with at least two of said circuits, from oscillating at the resonant frequency of one of said component tuned circuits, comprising means substantially increasing the power factor of said one component tuned circuit without substantially increasing the power factor of the composite tuned system.

2. An electric circuit arrangement for preventing a tuned system, composed of two seriallyconnected inductances and at least two condensers, one of which is effectively in shunt with both of said inductances and the other of which is effectively in shunt with only one of said inductances, from oscillating at an undesired frequency determined by said one inductance and its individual shunt condenser, so that instead the tuned system may oscillate at a desired freeuency determined by all of said inductances and condensers, comprising means for substantially increasing the power factor of the portion of the tuned system tending to oscillate at the undesired frequency wit-hout substantially increasing the power factor of the entire tuned system.

3. An electric circuit arrangement for preventing a tunable system, composed of two seriallyconnected inductances of substantially dierent value, a variable tuning condenser effectively in shunt with both said inductances and a fixed condenser of relatively small value effectively in shunt with said inductance of larger value, from oscillating when said tuning condenser is adjusted in the vicinity of its minimum value at a frequency determined by'said inductance of larger value and said fixed condenser, rather than at the frequenciesudetermined by both said inductances, said tuning condenser and said fixed condenser, comprising means for substantially' increasing the power factor for the portion of the system including said inductance of larger 3 microhenries (in air at 1000 cycles). 122 D0.

value and said fixed condenser without substantially increasing the power factor of the entire tunable system.

4. A composite tuned system comprising; a plurality of component tuned circuits having reactance elements individual thereto and a reactance element common with at least two of said circuits; and means for preventing said tuned system from oscillating at a frequency determined by less than all of said reactance elements, comprising means substantially increasing the power factor of at least one of said component tuned circuits without substantially increasing the power factor of the composite tuned system.

5. A tuned system comprising; a plurality of component tuned circuits having reactance elements individual thereto, and also a reactance element common to at least two thereof; and means for preventing said tuned system from oscillating at the resonant frequency of one of said component tuned circuits, comprising resistance means in said one tuned circuit effective to increase the power factor thereof to a value above that for the composite tuned system, said resistance means being so propoitioned and disposed with respect to the composite tuned system that said increase in the power factor of said one tuned circuit is effected without substantially increasing the power factor of the composite tuned system.

6. A tuned system comprising; two component tuned circuits having reactance elements individual thereto and a reactance element common thereto; and means for minimizing any tendency of said tuned system to oscillate at the resonant frequency of one of said component circuits rather than at the resonant frequency of the composite system, comprising resistance means effectively included in series in said one component circuit but substantially effectively external to the composite system and of such magnitude as to increase the power factor of said one componentcircuit to a value greater than the power factor of the composite system.

7. A composite tuned system comprising; two serially-connected inductances; a condenser effectively connected across said two serially-con nected inductances; a second condenser effectively connected across one of said inductances, said latter inductance and its associated condenser forming a component tuned circuit resonant at an undesired frequency; and means included in said component circuit for increasing the power factor thereof to a value greater than that of said composite tuned system to minimize any tendency of said system to oscillate at said undesired frequency.

8. A composite tuned system comprising; two serially-connected inductances of greatly different values; a condenser of relatively small capacitance'effectively connected across said two serially-connected inductances; a second condenser of relatively small capacitance effectively connected across the larger one of said inductances, said latter inductance and its associated condenser forming a component tuned circuit resonant at an undesired frequency; and means in said component tuned circuit for increasing the power factor thereof at said undesired frequency so that said tuned system oscillates prim-arily at its natural resonant frequency.

9. A composite tuned system comprising; two serially-connected inductances; a condenser effectively connected across said two serially-connected inductances; a second condenser effective- 1y connected across one of said inductances, said one inductance and its associated condenser forming a component tuned circuit resonant at an undesired frequency; and a resistance connected in series in the capacitive leg of said component circuit of such value as to increase the power factor of said component circuit to a value greater than that of the composite tuned system to prevent said system from oscillating at said undesired frequency.

10. A composite tunable system comprising; two serially-connected inductances; a variable condenser effectively connected across said two serially-connected inductances; a xed condenser effectively connected across one of said inductances, said latter inductance and said fixed condenser forming a component circuit resonant at an undesired frequency; and means included in said component circuit to increase the power factor of said component circuit, at the frequencies corresponding to the settings of said variable condenser in the vicinity of its minimum value, to a value greater than that of said composite system to insure that said system resonates primarily at the desired frequencies determined by said composite system instead of at the undesired frequency determined by said component circuit.

1l. A composite system tunable over given bands of frequencies, comprising; a plurality of series-connected inductance elements; a variable tuning condenser therefor; a relatively small xed condenser effectively in shunt with one of said inductance elements forming a component tuned circuit resonant at an undesired frequency near the upper limit of said band; and means for preventing said system from resonating at said undesired frequency when said system is tuned by said variable condenser in the vicinity of the upper frequency limit of said band without substantially impairing the response of said system when tuned to other portions of said band, comprising resistance means in the capacitance leg of said component tuned circuit proportioned to increase the power factor of said component tuned circuit to a value greater than that of said system when it is tuned in the vicinity of the upper frequency limit of said band.

12. A multi-frequency tuned system comprising; aplurality of reactance elements of one type; a plurality of reactance elements of opposite type; means selectively connecting said reactance elements into different groups of elements to form a plurality of tuned systems having different resonant frequencies, a one of said systems including a component tuned circuit having a natural resonant frequency; and means for attenuating the response of said tuned systems to the resonant frequency of said component tuned circuit without sumtantially impairing the responses of said tuned systems at their respective resonant frequencies, comprising means substantially increasing the power factor of said component tuned circuit without substantially increasing the power factors of any of said tuned systems.

13. A multi-frequency tunable system comprising; a plurality of inductance elements; a plurality of capacitance elements including a variable tuning condenser; means selectively connecting said elements into different groups of elements to form a plurality of systems tunable over different bands of frequencies, a one of said systems including at least two serially-connected inductance elements of which at least one is effectively individually shunted by a capacitance element thereby to form a component tuned circuit having a fixed natural resonant frequency; and means for attenuating the response of said tuned systems to the resonant frequency of said component tuned circuit without substantially impairing the responses of said tunable systems over their several tunable bands, comprising means substantially increasing the power factor of said component tuned circuit without substantially increasing the power factor of any of said tuned systems.

14. A system tunable over either of two bands of frequencies, comprising; two serially-connected inductance elements; a variable tuning condenser effectively in shunt with said seriallyconnected inductance elements; an aligning condenser effectively connected in shunt with one of said inductance elements; means for selectively effectively removing from circuit said aligning capacitance and the inductance element shunted thereby while leaving the other of said inductance elements in circuit; and means for attenuating the response of said system to the resonant frequency of the portion of said system including said aligning capacitance and the inductance element shunted thereby when in circuit, comprising a resistance included only in such portion of said system.

15. An oscillation generator comprising; a vacuum tube including input and output electrodes; a composite oscillation system connected to an input electrode of said tube comprising at least two component resonant -circuits having a common reactance element; a feed-back coupling from an output electrode of said tube to said oscillation system; and means for preventing operation of said oscillation generator at a frequency determined by less than all the reactance elements of said oscillation system, comprising means in at least one component circuit so proportioned and located therein as to increasethe power factor thereof toa value above that for said composite oscillation system.

16. An oscillation generator for generating waves of a given frequency comprising; a vacuum tube including input and output electrodes; a composite oscillation circuit connected to an input electrode of said tube including at least two reactance elements of each type and resonant as a Whole at said given frequency, at least one of said reactance elements of each' type being so proportioned and interconnected as to form a closed circuit resonant at an undesired frequency near said given frequency; a feed-back coupling from an output electrode of said tube to said oscillation system; and means for substantially impairing the operation of the generator at said undesired frequency without substantially impairing its operation at said given frequency, comprising means for increasing the power factor of said closed circuit to a value greater than that of said oscillation circuit as a whole.

17. A tunable oscillation generator comprising; a Vacuum tube including input and output electrodes; a tunable oscillation system for said tube connected to an input electrode thereof, said oscillation system including two serially-connected inductances of substantially different value, a variable tuning condenser effectively in shunt with both said inductances, and a fixed condenser of relatively small value effectively in shunt with said inductance of larger Value; a feed-back coupling from an output electrode of said tube to said oscillation system; and means, effective when said tuning condenser is adjusted in the vicinity of its minimum value, for preventing said oscillation generator from jumping from an operating frequency determined by all of the reactance elements of said system to a frequency determined by said inductance of larger value and said fixed condenser, comprising means for substantially increasing the power factor of the portion of the oscillation circuit including said inductance of larger Value and said fixed condenser to a Value greater than the power factor of the entire oscillation system.

18. A multi-range oscillation generator, comprising; a vacuum tube including input and output electrodes; an oscillation system for said tube connected to an input electrode thereof, said oscillation system including two series-connected inductances of different orders of magnitude, a variable condenser effectively in shunt with said series-connected inductances for operation over a lower frequency band, a small aligning condenser effectively in shunt with each of said inductances, ,and means for selectively effectively short-circuiting the inductance of larger magnitude whereby the oscillation generator operates over a higher frequency band; a feed-back coupling from an output electrode of said tube to said oscillation system; and means primarily effective when the oscillation generator is adjusted to oscillate at frequencies in the upper portion of the lower frequency band for preventing the frequency of the oscillations produced by the oscillation generator from jumping away from the resonant frequency determined by all the inductancesand capacitances then in circuit to a frequency determined by less than all such inductances and capacitances, comprising resistance means in the circuit of the aligning condenser for said inductance of larger value.

NELSON P. CASE. 

